The term “phenotype” is used to describe observable and measurable characteristics of an organism. For example, blue eyes are a phenotype, because they are clearly visible and they can be used to define an organism and learn more about it. Phenotypes are created through a combination of environment and genetic encoding; the genetic material of an organism is known as its “genotype.”

Many scientific studies have focused on phenotypes, because they can reveal interesting clues about organisms of all shapes and sizes. For example, some studies have attempted to figure out why many animals display a broad range of color variations, with people trying to figure out whether these variations are genetic, or caused by the environments these animals are raised in. The distinction between genotype and phenotype has also been used to discuss more complex ideas, like whether some people are fated to live particular lives, or whether they can be influenced by the environments they grow up in.

In order to be considered part of an organism's phenotype, a trait must somehow be observable or measurable. Blood type, for example, is a phenotype, even though you cannot actually see someone's blood type, because scientific tools can be used to determine blood type. Biochemical traits like secretions of various hormones are also considered to be phenotypes, expressions of an organism's genotype which can also be altered by the environment that the organism lives in.

You may also see organisms being classified together on the basis of their phenotypes. For example, many people consider blonde hair and blue eyes to be two aspects of the Scandinavian phenotype, since many Scandinavians exhibit these traits, while someone with dark skin, hair, and eyes might be considered to be an example of the African phenotype. The marked physical differences between these phenotypes are obviously genetic in nature, but they are also related to the environments that these people come from, as they are the result of centuries of evolution.

A phenotype can provide useful clues about an organism. For example, many people assume that creatures with hair are probably mammals, while creatures with feathers are birds, and things which are green are probably plants. When organisms are identified, a number of phenotypical clues are used to puzzle out the organism's identity, whether it be a variety of lichen or a type of bird.